The present invention generally relates to electrically conductive heated glass panel assemblies and control systems, for warming objects and for the removal of moisture on such glass panel assemblies. More particularly, the present invention relates to regulating the flow of current in low emissivity (low E) conductive metal oxide coatings on insulated glass (IG) panels and laminated structures. Most particularly, the present invention deals with the electrical connectivity to insulated glass panels, laminated structures, and combinations thereof.
At the present time, heating, cooking, moisture control, and the electrical control of such processes and activities do not take full advantage of the potential of the use of coated glass. In general, utilizing thin-film coatings to produce heat in a glass panel is an established concept. However, in the past, the film deposition techniques, such as those used in spray coating, were not precise, which resulted in non-uniform coatings and consequently imprecise heating. Recently, the depositing of the coatings has improved, for example, through the use of chemical vapor deposition (CVD), but the electrical control of and connectivity to the coatings has not.
An application of heated glass that has seen these changes over the last thirty years is, for example, the commercial refrigerator and freezer doors in supermarkets, where a tin oxide coating is disposed on one of the interior surfaces of an IG panel and where an electric current is dissipated in the tin oxide to provide heat to raise the glass temperature above the dew point. On such doors, the heat eliminates the formation of condensation, so that employees and customers can view the refrigerator/freezer contents after individuals have opened and closed the doors.
However, non-uniform coatings and traditional electrical control methods result in wasted energy, produce hot and cold spots on the glass, and can result in safety hazards should the glass break and expose the current-carrying film. This approach could benefit from control opportunities that exist using the current state of control technology.
For transportation applications, where heated windows and mirrors provide drivers and occupants of land, air, and water vehicles unimpeded viewing by the removal of condensation, breakage of the electrically heated glass panels can also result in electrical safety problems. Underwriters Laboratories (UL) has expressed interest in improving the breakage of electrically heated glass panels and consequently the exposure of live electrical conductors within the glass.
In convenience stores and delicatessens, sandwiches and other food items are kept warm in glass enclosed food warmers, through the use of base electrical element heaters. The use of glass enclosures-does allow the contents to be seen, but the use of only base-electrical ribbon element heaters does not allow for radiant heating techniques that would be advantageous for the warming of food items from an area above the food items.
Commercial buildings, sports stadium skyboxes, sloped glazing in atria, canopies, and general fenestration applications, could benefit from the use of electrically heated glass panels, but the underlying reason for the reluctance to adopt these technologies in architectural applications is the lack of an integrated connection circuit and a systems approach to these applications. Expanding the adoption of these technologies, however, is hampered by the complexity of safely, reliably, and cost effectively combining glass and electricity.
There have been many methods advocated to electrically control heated glass panels. Among them are: direct connection to 120V AC power, use of step-down transformers, resistor-capacitor (RC) networks, triacs, and control circuits that directly drive resistive loads. All of these approaches have their benefits and also their disadvantages.
Some of the problems that must be overcome by the electrical controls are: (a) electrical shock potential, (b) circuitry components releasing significant heat to the overall system, (c) overload of the integrated connection circuits that supply the power to the panels, (d) bulkiness of the parts used in the control method, (e) lack of mounting space for the parts, (f) electrical interference generated by the control method, (g) lack of predictability and complexity of the control method, and (h) overall serviceability and costs.
The RC network approach that is taught in U.S. Pat. No. 5,852,284 to Teder et al. uses an RC circuit in series with the conductive coating on the glass to match the power supply with the characteristics of the glass assembly. Typically the value of the capacitor can be chosen for the desired power density via known electrical engineering calculations. In this method, the capacitor functions by changing the phase angle between the voltage and current of the applied AC voltage, hence regulating the power dissipation.
Disadvantages of this method are that capacitors of the required value are: (1) physically large and may be expensive, (2) when a capacitor fails, the full line voltage may be applied across the coated glass, (3) there is no integrated protection using such a method, so over-current protection must be provided, (4) handling many different applications is problematic, such that either a stock of a large number of different values of capacitors would be required or a large number of series-parallel networks must be constructed, which can also complicate the issues of required space and cost, and (5) the varying electrical phase angle may present power quality problems.
The use of triacs has shown promise as a way to vary the current that is applied to electrically coated sheets of glass. Examples of triac use are U.S. Pat. No. 4,260,876 to Hochheiser and U.S. Pat. No. 5,319,301 to Callahan et al. However, this use must overcome the negative effects of the triacs generating high peak currents, high harmonic distortion, and electromagnetic interference (EMI).
The use of electrical control circuits to operate the triacs, which in turn controls the current through the electrically conductive heated glass panel assembly and control systems, has the potential to minimize these negative effects, but to-date it has not been able to accomplish that task. Consequently, the application of triacs has not fully been able to solve the aforementioned problems in the control of electrically conductive heated glass panel assembly systems.
Also, the interconnections between the parts of an electrically conductive heated glass panel assembly and control system have typically been treated as individual parts and not as part of an overall system. In some cases, the bus bars have been screen-printed or fired conductive silver frits. These are difficult and expensive to print and difficult to solder external leads to, where special solder is required.
Further, various metallic tapes, including copper, have been attached to glass using adhesives but these connections exhibit poor adhesion to the glass. Also, rigid electrical terminations at the edge of the glass result from these methods of applying the bus bars, which makes them vulnerable to mechanical flexing, can expose them to condensation, and typically are expensive.
U.S. Pat. No. 2,235,681 to Haven et al., teaches the attaching of metal bus bars to a glass sheet as it applies to structural solder elements-but not for electronic control systems.
Producers of crystalline solar cell technology (also referred to herein as photovoltaic technology) have been seeking ways to deposit metal-on-glass. U.S. Pat. No. 6,065,424 to Shacham-Diamand et al., teaches thin metal film coatings sprayed onto glass by the use of an aqueous solution and subsequent annealing of the coatings. In U.S. Pat. No. 4,511,600 to Leas, a conductive metal grid is deposited atop a crystalline solar cell by the use of a mask and orifices (without the use of gas or air pressure to impart dispersion or velocity to the metal particles). The '600 patent also advocates the use of a powdered metal that is heated to a molten temperature in a refractory crucible.
In U.S. Pat. No. 4,331,703 to Lindmayer, a conductive metal is flame sprayed onto a silicon solar cell. In U.S. Pat. No. 4,297,391, also to Lindmayer, particles of a material are formed at a temperature in excess of the alloying temperature of the material and the silicon, and then the two are sprayed onto the surface of the glass at a distance, which causes the material and the silicon to firmly adhere to the surface. The '391 patent also teaches the use of a mask.
Currently, the control of electricity to electrically conductive glass panels centers primarily on control of the heating elements and not on monitoring system parts or the entire heating system for safety, power matching, or the like. For wiring installation purposes of the glass panels, it is common for holes to be drilled in the glass panels at the time of manufacturing and in the framework at the time of installation as well as for termination of wiring that is done in the field.
When the assembly of the electrical panels is completed, some of the controls, wiring, and associated parts are visible to users of these panel systems. Since power supply matching for each application is statically performed, the changing of system variables after manufacturing is, at best, cumbersome, while monitoring of system operating conditions is nearly nonexistent.
Termination of system wiring to existing facility electrical services, as well as on-site glazing operations, is not done with a total systems approach in mind. Thus those skilled in the art continued to seek a solution to the problem of how to provide a better electrically conductive heated glass panel assembly and control system, and a method for producing the panels.